Outcast £3.89 @ GOG

Sorry for earlier post. This is a quid cheaper than steam and it comes with Bonus content including the soundtrack (3.99 on steam), Artwork, Behind the scenes, out takes and DRM free!

Taken from wikipedia:

"Outcast was named the "Adventure Game of the Year" by GameSpot [In 1999]. Writing in 2009, GamesRadar praised the game as "revolutionary", noting that its freedom to explore a three-dimensional open world preceded Grand Theft Auto III by two years, and that allowing the player to pick and choose missions in an order that suited their playing style came nine years before Fallout 3."

Fair warning: A lot of bugs reported in early reviews but it's worth purchasing for nostalgia and to support the developer.

Wow, a blast from the past. My PC at the time really struggled to run this, it used Voxel type of technology or something, instead of 3D acceleration if I recall - so your CPU had to do a lot of the work. It looked stunning at the time. Looks like they have enhanced the engine... If this now supports higher resolutions, it could look stunning even now.